The present invention relates to a piston type compressor having a housing which includes a cylinder head defining a discharge chamber, and a seal member for sealing an inside of the cylinder head, and more particularly to a piston type compressor having a housing which defines a suction chamber and a crank chamber accommodating a cam for converting rotation of a rotary shaft to reciprocation of a piston, wherein gas introduced from the suction chamber into a compression chamber is compressed and discharged to the discharge chamber in conjunction with the reciprocation of the piston.
A piston type compressor for use in a vehicle air conditioner includes a double-headed type piston, as disclosed in Unexamined Japanese Patent Publication No. 7-63165. As shown in FIG. 5, the piston type compressor includes a front cylinder head 101 and a rear cylinder head 102. The front cylinder head 101 defines a discharge chamber 111A. The rear cylinder head 102 defines a suction chamber 112 and a discharge chamber 111B. The piston type compressor further includes a pair of cylinder blocks 104A, 104B. The front cylinder head 101 and the rear cylinder head 102 are connected to the cylinder blocks 104A, 104B through gaskets 103A, 103B, respectively. Namely, the front cylinder head 101, the rear cylinder head 102 and the cylinder blocks 104A, 104B cooperate to form a housing of the piston type compressor. Front compression chambers 113A are defined in the front cylinder block 104A by pistons 114. Rear compression chambers 113B are defined in the rear cylinder block 104B by the pistons 114.
Radially outer portions 103a of the respective gaskets 103A, 103B seal the discharge chambers 111A, 111B from the atmosphere outside the compressor at respective joints between the cylinder heads 101, 102 and the cylinder blocks 104A, 104B.
Suction valve devices 115A, 115B for the front and rear compression chambers 113A, 113B are provided by rotary valves 117A, 117B, respectively. The rotary valves 117A, 117B are formed in a rotary shaft 116 in such a manner that a gas passage between the respective compression chambers 113A, 113B and the suction chamber 112 is opened and closed alternately by rotation of the rotary shaft 116. Part of the gas passage is formed by an axial passage 116a which extends axially in the rotary shaft 116. Refrigerant gas is introduced from an external refrigerant circuit into the suction chamber 112 in the rear cylinder head 102. The refrigerant gas in the suction chamber 112 is then drawn into the front and rear compression chambers 113A, 113B through the axial passage 116a of the rotary shaft 116 and the rotary valves 117A, 117B, respectively.
It is noted that the piston type compressor has the suction chamber 112 formed in the middle portion of the rear cylinder head 102, surrounded by the discharge chamber 111B, for the purpose of simplifying the structure of connection between the axial passage 116a and the suction chamber 112.
In the above-described piston type compressor, the outer sealing portions 103a of the gaskets 103A, 103B at the respective joints between the cylinder heads 101, 102 and the cylinder blocks 104A, 104B are exposed to a large pressure difference between high pressure of refrigerant gas in the discharge chambers 111A,111B and the low atmospheric pressure. Accordingly, the outer sealing portions 103a of the gaskets 103A, 103B should have sufficient heat and pressure resistance in order to prevent the refrigerant gas from leaking out from the discharge chambers 111A, 111B, which leads to increased manufacturing cost.
Particularly, in the piston type compressor disclosed in the Unexamined Japanese Patent Publication No. 7-63165 in which the rotary valves 117A, 117B serve as the suction valve devices 115A, 115B, respectively, the refrigerant gas from the external refrigerant circuit is distributed to the front and rear rotary valves 117B, 117A through the suction chamber 112 which is formed in the rear cylinder head 102. Accordingly, the front compression chambers 113A are located farther from the suction chamber 112 than the rear compression chambers 113B.
Thus, the front compression chambers 113A tends to be short of the refrigerant gas to be introduced into the front compression chambers 113A thereby to increase compression ratio, so that temperature of the refrigerant gas discharged to the discharge chamber 111A rises in comparison to that of the refrigerant gas discharged to the discharge chamber 111B. As a result, the outer sealing portion 103a of the gasket 103A for shutting communication between the front discharge chamber 111A and the atmosphere tends to be more susceptible to the influence of heat than the similar outer sealing portion 103a of the gasket 103B for the rear discharge chamber 111B. Therefore, there is a need for providing a piston type compressor that reduces a load on a seal member for sealing the cylinder head of the compressor.